The present invention relates to the automated material analysis arts. It finds particular application in conjunction with the automatic measurement of cut growth in rubber and will be described with particular reference thereto. However, it is to be appreciated that the invention may also find application in conjunction with other kinds of crack testing, flex testing, and other kinds of failure testing in rubber, elastomers, and other materials.
Heretofore, cut growth measurements were commonly made manually. That is, a plurality of rubber samples were mounted at their opposite ends to a pair of parallel bars. One of the bars was reciprocated such that the rubber samples were cyclically stretched. Periodically, e.g. every four hours, the cyclic stretching was stopped and the length of each cut was measured manually, typically with an optical microscope.
One of the problems with this procedure was that manual measurement was relatively slow. When a large number of samples were tested concurrently, e.g. two dozen samples, the manual cut measurements could take a couple hours.
Another problem with this manual technique is that the cyclic rubber deformation was stopped during the manual cut measurements, as well as at night and over weekends. The long pauses in the cyclic elongation raised questions regarding whether the rubber samples were to relax sufficiently that viscoelastic effects altered the test results.
Commonly, the cuts grew very slowly, if at all, for a long period, typically many days. Once a cut started to grow, failure could occur quickly, e.g. overnight. Accordingly, the tests could not be allowed to run unattended, absent the continuous presence of laboratory personnel. Moreover, the relatively long intervals between measurements were reduced as failure started to occur. These shorter time interval samplings could be every hour or even twenty minutes or less. Because the plurality of samples were flexed concurrently, it was necessary to stop the flexing of all samples while the failing sample was measured more frequently.
One attempt to automate the test procedure is illustrated in U.S. Pat. No. 4,574,642, issued Mar. 11, 1986. One drawback of the disclosed test apparatus is that it tested only a single rubber sample. Because the test apparatus could only test one sample at a time, the test cost per sample was relatively high. This apparatus utilized a line scan camera, i.e. a single linear array of photodiodes to monitor cut length. More specifically, the cut length was determined by integrating the output of the illuminated diodes. The resultant analog voltage signal had an amplitude varied in accordance with the number of photodiodes illuminated by light passing through the cut. The use of a one dimensional array limited the measurement to relative cut length rather than length of the cut relative to the width of the sample.
The analog voltage signal oscillated as the sample stretched and contracted. Although each voltage peak was indicative of cut length, inherent voltage drift rendered the peaks inaccurate as a measure of absolute length.
The present invention provides a new and improved analysis system and technique which overcome the above referenced problems and others.